The present invention relates to a method and apparatus for receiving a material web traveling at a first speed in a receiving zone, forming discrete parts from the material web, and applying the discrete parts onto a carrier traveling at a second speed through an application zone.
Disposable absorbent articles, such as disposable diapers, generally, have been manufactured by a process where discrete parts or components of different materials, such as leg elastic, waist elastic, tapes and other fasteners have been applied to a continuously moving carrier. Often, the speed at which the parts are fed from one place in the process onto a carrier is different from the speed of the carrier; therefore, the speed of the parts must be changed to match the speed of the carrier to properly apply the parts without adversely affecting the process or the finished product.
Similarly, labels are typically placed onto articles when the speed at which the labels are fed into the process is not the same as the speed of the article to be labeled. Thus, the speed of the labels must be changed to match the speed of the carrier to properly apply the parts without adversely affecting the process or the finished product.
Several different conventional methods for changing the speed of a part or component of material such that it can be applied to a continuously moving carrier have been known to those skilled in the art.
For example, one known method is commonly referred to as the xe2x80x9cslip cutxe2x80x9d or xe2x80x9ccut and slipxe2x80x9d method. A web of material, which is traveling at a slower speed than the carrier, is fed into a knife and anvil roll having a surface speed equal to speed of the carrier. The material slips against the surface of the anvil roll until the knife cuts it into discrete parts. The purpose of the slip is to ensure the correct amount of material is metered into the system at the desired tension prior to cutting. As the material is cut into the discrete parts, vacuum in the anvil roll is activated to hold the discrete part on the anvil without slipping, so that the discrete part is accelerated to the speed of the anvil roll. The anvil roll then carries the part to the point where the vacuum is released and the parts are applied to the carrier while both the parts and the carrier are traveling at the same speed. The problem with the above method is that the slip process is very sensitive to material properties and process settings. For example, when the coefficient of friction between the material and anvil roll is too high, the material will elongate during the slip process. This elongation, if it occurs, can contribute to high variability in the final cut length and placement of the discrete part on the carrier.
Another method has used festoons to reduce the speed of the carrier to match the speed of the discrete parts of material to be applied to the web. An example of this method is described in U.S. Pat. No. 5,693,195 issued to Schmitz. The carrier is temporarily slowed down to the speed of the parts with the excess portion of the carrier gathering in festoons. The parts of material are then applied to the carrier while both the parts and the web are traveling at the same speed. The festoons are then released allowing the moving web to return to its original speed. This method has two main drawbacks. First, the carrier must be festooned and then released; this may damage or otherwise change the properties of the carrier. Second, the storage system requires a large amount of space in typical disposables production systems because there is a direct relationship between line speed and storage space needed.
Another method has utilized a cam actuated follower arm. The cam actuated follower comprises a cam follower at one end of the arm and a holding plate at the other end of the arm. The cam follower remains in contact with a fixed cam which is mounted concentric with the instantaneous center of rotation of the holding plate. As the holding plate rotates, its radial distance from the center of rotation is increased and decreased to change the surface speed of the holding plate. The discrete parts of material are placed on the holding plate when it is at its smallest radius so that the speeds match. The plate then extends radially enough during the rotation to match the speed of the plate to the speed of the carrier. At this point the discrete parts are transferred to the carrier. This method has two main drawbacks. First, the plate is designed to match the curvature of one radius, not both. This means that either the pick-up of the discrete part or the transfer of the discrete part, or both, will occur across a gap for some part of the transfer. This can lead to a loss of control of the discrete part, which impacts handling of parts under tension, such as leg elastics. Second, to achieve the desired change in speed, the mechanical elements typically used, such as cams or linkages, become fairly large to stay within acceptable design limits for accelerations and rise angles. This size leads to increased cost and reduced flexibility, as the unit must be redesigned for each application.
Another method has utilized noncircular gears to change the speed of a transferring device. The means rotate at a constant radius, but the rotational velocity is varied between a minimum and a maximum to pick up the discrete part at its speed and place the part on the carrier at its speed. This eliminates the size issues and speed or gap mismatch issues, but relies on mechanical means to achieve the change in rotational velocity. The drawback of this is that new transmission parts (gears or other means) are required each time a change in product design occurs that changes placement pitch length, discrete part length, or other key factors. This can be expensive and time-consuming to change. An example of this method is described in U.S. Pat. No. 6,022,443 issued to Rajala and Makovec.
Another method is commonly referred to as a servo part placer. This apparatus functions, similar to the cut-and-slip method described above except that it attempts to match a first speed of the material web when receiving the part and a second speed when placing the part onto a carrier. In a first prior art embodiment, a cutting blade is used to sever the material web against an anvil roll and then the anvil roll transfers the discrete part to a transfer head for subsequent application onto the carrier. While the use of anvil roll, instead of severing against transfer heads, allows for the transfer heads to be more lightweight, the use of anvil roll has difficulties in the continuous application of adhesive to the material web because the discrete part would adhere to the transfer head. In a second prior art embodiment, a cutting blade is used to sever the material web directly against a transfer head and the transfer head then applies the discrete part to the carrier. While this embodiment allows for the continuous application of adhesive to the material web, it does sever against the transfer heads which requires them to be sufficiently rigid (and ultimately heavy) to sustain the impact of cutting blade. Consequently, the heavier transfer heads create higher inertia that ultimately requires the use of high torque motors.
What is needed is a servo part placer apparatus that is capable of continuous application of adhesive to the material web and which does not sever against the transfer heads (herein referred to as shells) such that smaller motors that fit well into the apparatus"" mechanical design may be used.
An apparatus and method for receiving a material web traveling at a first speed in a receiving zone, forming discrete parts from the material web, and applying the discrete parts onto a carrier traveling at a second speed through an application zone. The apparatus has a cutting device for severing the material web to form the discrete parts. At least two shells for receiving the discrete parts in the receiving zone and applying the discrete parts in the application zone are used. The shells may be coupled to programmable motors for moving said shell in an orbital path. The programmable motors and shells may be aligned in relation to a common axis. The programmable motors maintain said shells at first surface speeds in the receiving zone as said shells pick up the discrete parts and maintain said shells at second surface speeds in the application zone as said shells apply the discrete parts to the carrier. A roll may be positioned interior to said shells. The cutting device may be used to sever the material web between said shells and against said roll. The roll may be a vacuum roll that provides vacuum in order to hold the discrete parts against said shells. The cutting device may be a cutting roll having an adjoining cutting blade which together rotate with or about a cutting roll shaft. The cutting device may rotate at a cutting surface speed substantially equal to a velocity of the material web while each of the discrete parts are being severed and formed and at a different cutting surface speed during intervals between discrete parts being severed and formed from the material web.
The first surface speeds of said shells may be substantially equal to the first speed of the discrete parts in the receiving zone and the second surface speeds of the shells may be substantially equal to the second speed of the carrier in the application zone. Additionally, the first and second surface speeds of said shells may be substantially constant. Alternatively, the first and second surface speeds of said shells may be variable. Alternatively, either the first surface speeds of said shells or the second surface speeds of said shells may be variable.
The programmable motors may be a programmable motor selected from the group consisting of a motor having a hollow shaft, a linear motor having a stationary track rail, a motor having a rotatable outer rotor and a stationary inner stator, and a motor having a rotor rotatable around a stationary component of a motor. The programmable motors are located on at least one stationary central shaft coaxially with the common axis.
The shells may have an axial length from about 4 cm to about 200 cm, tangential width from about 0.5 cm to about 200 cm, and a thickness from about 0.25 mm to about 3 mm. The shells may be constructed from materials including, but not limited to, plastic, aluminum, steel, and combinations thereof. The shell may hold the discrete parts by vacuum, mechanical forces, electrostatic forces, magnetic forces, and combinations thereof.
An applicator for performing a secondary process on the parts between the receiving zone and the application zone may be used. An applicator for performing a secondary process on the parts before the receiving zone may also be used. The secondary process may be the application of adhesive or printing.
The carrier may be selected from the group consisting of a web substrate, belt, drum, and external-discrete part.